Segmentation of low‐cost high efficiency oxide‐based thermoelectric materials

Abstract

Thermoelectric (TE) oxide materials have attracted great interest in advanced renewable energy research owing to the fact that they consist of abundant elements, can be manufactured by low-cost processing, sustain high temperatures, be robust and provide long lifetime. However, the low conversion efficiency of TE oxides has been a major drawback limiting these materials to broaden applications. In this work, theoretical calculations are used to predict how segmentation of oxide and semimetal materials, utilizing the benefits of both types of materials, can provide high efficiency, high temperature oxide-based segmented legs. The materials for segmentation are selected by their compatibility factors and their conversion efficiency versus material cost, i.e., "efficiency ratio". Numerical modelling results showed that conversion efficiency could reach values of more than 10% for unicouples using segmented legs based p-type Ca 3 Co 4 O 9 and n-type ZnO oxides excluding electrical and thermal losses. It is found that the maximum efficiency of segmented unicouple could be linearly decreased with increasing the interfacial contact resistance. The obtained results provide useful tool for designing a low-cost and high efficiency thermoelectric modules based-oxide materials.

Segmented Thermoelectric Oxide‐Based Module for High‐Temperature Waste Heat Harvesting

“…As presented in Figure 3, the maximum efficiency of STEGi ncreases sharply upon increasingt he A p /A n ratio,r eaching am aximum of 2.7% at A p /A n = 2.4 and then decreases slowly above this value.A sf or the NTEG,t he maximum efficiency attains 1.6 %a tA p /A n = 3.5. These results suggest that the STEG would performw ith the maximum efficiency,w hich is approximately 1.7 times higher than that of the NTEG at their respective optimized A p /A n ratios.W ith the same input TE data and boundary conditions, both the resultso btained by the exact solution 1D model [5] and the finitee lement 3D [21] model are in good agreement, as clearly shown in Figure 3. Upon combining with n-legs of Zn 0.98 Al 0.02 O, both the STEG and NTEG have an efficiency of less than 3%.…”

“…By this approach, we have successfully demonstrated a4 -couple thermoelectric generator (TEG) using p-segmented legs of Ti 0.3 Zr 0.35 Hf 0.35 CoSb 0.8 Sn 0.2 and misfit-layered cobaltite Ca 3 Co 4 O 9 + d ,a nd n-legs of 2% Aldoped ZnO with an improved output power density of more than three times as compared to the non-segmented oxide TEG.T he high performance of the segmented TEG (STEG) also benefitted from the reduction in the total internal resistance of the module due to the low contact resistance of the half-Heusler alloy and the Ag electrodes.A part from the high output power density,the long-term stability test implies the potential implementation of the segmented oxide module in applications of power generation from waste heat at high temperatures.T of urther improve the conversion efficiency of the oxide-based TEG,abetter performanceo ft he n-type material is needed. Dually doped ZnO [8] or its segmentation with the n-type half-Heusler alloy [5] could be as olution. …”

“…[3,4] In addition, TEGs made of oxides are cost-effective due to the fact that the materials are cheap and easily processed. [4,5] AmongT Eo xides,t he layered-cobaltite Ca 3 Co 4 O 9 + d (Ca349) and doped ZnO materials have been intensively investigated and considered as promising candidates for high-temperature applications. [6][7][8] Although ac onsiderable number of oxide-based TE modules have been fabricateda nd characterized, the output power generation of oxide modules are still limited due to the low performance of oxide materials,i np articular in the mid-tolow temperature range,a nd the large internal resistance.…”

“…[10,15] From the materials TE properties as af unctiono ft emperature,t he efficiencies of segmented and non-segmented legs/ TEGs were calculated using the theoretical modeld escribed in Ref. [5].I nt his model, the materials for segmentation are selected based on their figure of merit (zT)a nd compatibility factor (s ¼ ffiffiffiffiffiffiffi ffi…”

In Operando Study of High‐Performance Thermoelectric Materials for Power Generation: A Case Study of β‐Zn4sb3

“…The development of TE materials has made an impressive progress [1,3,4] with the high values of zT achieved in many materials such as zT = 2.6 at 923 K for tin selenide [5] , zT = 1.5 at 1200…”